Liquid CO.sub.2 is utilized to form CO.sub.2 snow for the purpose of pre-chilling insulated containers in which perishables to be stored or shipped at reduced temperatures may be received. In this manner, such insulated containers may be stored or shipped over reasonably long periods of time while the contents of the containers are held at reduced temperatures independent of attendant mechanical refrigeration equipment.
At present, CO.sub.2 snow is formed as a result of liquid CO.sub.2 under pressure being supplied to the interior of a generally bell-shaped head or nozzle and discharged through small lateral ports from a position disposed centrally within the head toward the internal surfaces thereof. The sudden reduction of pressure of the liquid CO.sub.2 results in CO.sub.2 snow being formed and being discharged from the open outer end of the bell-shaped head. These bell-shaped nozzles or heads are capable of producing one pound of CO.sub.2 snow for each 2-1/4 to 2-1/2 pounds of liquid CO.sub.2 supplied to the head. It may thus be seen that the weight of CO.sub.2 snow produced is considerably less than half of the weight of the liquid CO.sub.2 required to produce the snow.
Accordingly, a need exists for a CO.sub.2 snow producing nozzle or head which will be effective to produce a greater volume of CO.sub.2 snow per unit of liquid CO.sub.2 utilized to produce the CO.sub.2 snow.
Examples of various forms of CO.sub.2 snow forming heads and other similar structures including some of the general structural and operational features of the instant invention are disclosed in U.S. Pat. Nos. 2,978,187, 3,109,296, 3,815,377, 3,861,168, 3,922,878, 3,932,155 and 4,111,362.